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\(x-\left(21-x\right)=x+9\)
\(\Leftrightarrow x-21+x-x=9\)
\(\Leftrightarrow x=9 +21=30\)
\(x-\left(21-x\right)=x+9\)
\(\Leftrightarrow x-21+x=x+9\Leftrightarrow2x-21=x+9\)
\(\Leftrightarrow2x-x=9+21\Leftrightarrow x=30\)
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a,\(2x+12-18=x+4-18\)
\(\Rightarrow2x-x=4-1+18-12\)
\(\Rightarrow x=9\)
b,\(-5x+10-102=-6x-102\)
\(\Rightarrow-5x+6x=-102+102-10\)
\(\Rightarrow x=-10\)
a, 2x + 12 - 18 = x + 4 - 18
2x -x = 4 - 18 - 12 + 18
x = - 8
b, - 5x + 10 - 102 = - 6x - 102
- 5x + 6x = -102 - 10 + 102
x = - 10
VERY GOOD!!!
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a) \(7-x=8-\left(-7\right)\)
\(\Leftrightarrow-x=8+7-7=8\)
\(\Leftrightarrow x=-8\)
Vậy x = - 8
b) \(x-8=\left(-3\right)-8\)
\(\Leftrightarrow x=\left(-3\right)-8+8\)
\(\Leftrightarrow x=-3\)
Vậy x = - 3
a) 7 - x = 8 - (-7)
\(\Rightarrow\) 7 - x = 8 + 7
\(\Rightarrow\) -x = 8
\(\Rightarrow\) x = -8
Vậy: x = -8